1. Field of the Invention
The invention relates to a solid absorber apparatus for a cyclic absorption process, and more particularly to a solid absorber apparatus having a single vapor region so that absorption and desorption of a given portion of coolant vapor takes palce across the same surface of the solid absorber material.
2. Discussion of the Art
In a cyclic absorption process, a coolant in vapor form is fed to the absorber material serving as the operating means in an absorber and is there absorbed or adsorbed, releasing absorption or adsorption heat. This reaction heat is removed by means of a cooling heat exchange medium. The absorber material can be regenerated by adding heat by means of a heating heat exchange medium. During the regeneration process, the coolant is expelled, liquefied in a connected condenser and fed under reduced pressure to an evaporator from where the coolant can be returned, after evaporation, to the regenerated absorber in the cyclic process. Such a cyclic process can be utilized in various ways. The best known way is its use as an absorption heat pump, as an absorption refrigeration machine or as a heat transformer.
Such a cyclic absorption process can be operated continuously with liquid absorber materials or discontinuously, particularly periodically, with solid absorber materials. The invention relates to the latter case. Modern-day pairings of solid absorber and coolant are, for example, zeolite and water or ammonia. The solid absorber according to the invention is intended, in particular, for use with such pairings. Zeolites and comparable solid absorbers are distinguished in that, during the absorption process (hereinafter, the term absorption is intended to always include adsorption as well) and during the desorption process, they retain their geometric structure, particularly their granular or sausage shape and will not swell even during the absorption of coolant. The invention relates particularly also to solid absorbers operating with constant volume solid absorber materials.
In principle, there are two structural types of solid absorbers. In the first structural type, the coolant vapor is fed to the solid absorber material at one side and is removed from the solid absorber material on the opposite side. Thus two different vapor regions are provided for absorption and desorption of the coolant. The invention relates to the second structural type wherein the coolant is fed to the solid absorber material from a single vapor region to the middle of the depth of the chambers or chamberlike zones which contain the solid absorber material and travels back again. Thus, a single vapor region serves alternatingly as the absorber vapor region and the desorber vapor region. This second structural type has advantages, starting with the elimination of the second vapor region.
From the multitude of applicable prior art, the solid absorber according to U.S. Pat. No. 4,034,569 is cited as but one example.
For solid absorbers, the following different requirements should all be met at the same time, if possible, in the most optimum manner:
1. Mass transfer between coolant vapor and solid absorber material during the absorption process as well as during the desorption process should take place as unimpededly and quickly as possible and should cover the entire available mass of solid absorber material. This requires, inter alia, the least possible pressure loss along the vapor region as well as [only] small pressure differences between the surface of the solid absorber material facing the vapor region and regions disposed further back. PA0 2. The flow, or current, of heat to the cooling heat exchange medium during the absorption phase as well as the transfer of heat from the heating heat exchange medium during the desorption phase are to take place as quickly and effectively as possible because heat losses, in particular, are undesirable, and large-area heat exchange surfaces lie as closely as possible to all regions of the solid absorber material, which itself generally is a relatively poor heat conductor. PA0 3. Notwithstanding Requirements 1 and 2, the thermodynamic efficiency of the solid absorber is to be optimized at minimum expense for heat exchanger masses with reference to the given quantity of solid absorber material. PA0 4. The design of the solid absorber is to make it possible to meet Requirements 1 through 3 equally well, independently of the dimensions of the solid absorber with respect to the solid absorber material.
The known solid absorbers of the second structural type considered by the invention meet these various requirements only in an imbalanced manner.
The species to which the invention relates is a refrigerator made by Homann-Werke, Wuppertal, as described in FIGS. 257 and 258 of the monograph by R. Plank/Kuprianoff, entitled "Die Kleinkaltemaschine" [The Small Refrigeration Machine], published by Springer Verlag Berlin, Gottingen, Heidelberg, 2nd Revised Edition, 1960, pages 351-359, particularly beginning at page 355, No. 3. The system of calcium chloride and ammonia is used as the operating medium-coolant pair. The calcium chloride is filled into elongate vertical chambers whose upper frontal faces are open and which are formed of stamped and welded-together steel sheet. The ammonia vapor fills a vapor region composed of exposed frontal sections of the chambers. The surface area of the chamber system is enlarged considerably by welded-on ribs and is alternatingly charged with cooling air and with hot air heated by a burner system. Calcium chloride swells during the absorption of ammonia; therefore, the chambers can be filled only partially (see German Pat. No. 554,766, page 2, lines 62-70). The heat exchanger itself, which forms the chambers, has the shape of an upright plate whose large vertical dimension defines the depth of the chambers and whose large horizontal dimension width defines the direction in which the adjacent chambers follow and whose second, small horizontal dimension represents the length between the exterior surfaces that are charged with heat exchange medium. This length can only be small since otherwise the flow of heat from the exterior faces charged with the heat exchange medium through the exterior chamber walls into the solid absorber material would no longer be sufficient. Thus the above-mentioned Requirement 4 can no longer be realized, i.e. the prospect for unlimited expansion of the system in the direction of the above-mentioned (short) length. System expansion is possible only in the width direction since expansion in the depth direction would also contradict the above Requirement 1. Moreover, the aspect of not permitting pressure losses through the vapor region which is part of this requirement is not met satisfactorily in this prior art arrangement since all of the separate vapor regions must be fed from one conduit system above the individual chambers which makes it difficult to prevent pressure losses along the length of the vapor region. If the chambers are excessively deep, moreover, undesirable additional pressure losses would occur in addiion to the insufficient mass transfer.
To obtain more compact structural units, it has been attempted, by way of various configurations, to give the heat exchanger a cylindrical shape. In solid absorbers of a different species, as disclosed in German Pat. No. 612,169 and German Pat. No. 814,158, which likewise goes back to the Homann-Werke, circular disc shaped or circular ring shaped metal supporting sheets were arranged vertically above one another. In this arrangement of a different species, in which no individual juxtaposed chambers are provided, the outer faces of the cylinder and possibly a cylindrical core recess are charged with the heat exchange medium. For the same reason as in the solid absorber of the species of the invention, the radial expanse of the heat exchanger, which corresponds to the length of the solid absorber of the species of the invention, is limited. Requirement 4 cannot be met as well since completely new heat exchangers with different radii have to be built if the solid volume is enlarged. Moreover, doubts continue to exist regarding the other mentioned criteria, particularly the pressure gradient.
In another known cylindrical configuration according to German Pat. No. 554,766--already mentioned in connection with the calcium chloride-ammonia system--wherein the cylinder axis is arranged horizontally, swelling solid absorber material is clamped in between a series of annular metal sheets. This clamped together assembly is introduced, with play to accommodate the increase in volume due to swelling, into a heat exchange body having laminar ribs on its exterior. The play volume simultaneously forms the vapor region. A centrally inserted resistance heating rod serves as the heating heat exchange medium, a stream of air charging the ribs on the cylindrical heat exchanger body serves as the cooling heat exchange medium. The predominant supply and removal of heat here takes place at the frontal faces of the chambers formed between the annular metal sheets. Heat transfer from the radially inwardly disposed frontal face is here inhibited in that this frontal face has the smallest surface area compared to the remaining outer chamber area. External cooling is thus impaired since heat conductive contact over the entire circumferential face of the chambers with the externally ribbed heat exchange body can be established only after the solid absorber material has swelled completely and then the heat conduction between the outer heat exchanger and the inner parts of the metal sheets is still impaired due to the poorly [heat] conducting solid absorber mass which lies therebetween, at least in a large circumferential region. Once the absorber material has swelled, the vapor region is also filled substantially by a porous mass, which does not return to its original volume, between the metal sheets and thus results in considerable pressure reductions in the vapor region.
All of the known solid absorbers considered above are relatively old. In the meantime, the stated drawbacks have resulted in stagnation of the applicable art. More recently, attempts have been made to again master these difficulties without, however, arriving at a convincing solution. The most recent state of the art is disclosed in DE-OS No. 3,016,290. Here, plate-shaped structural units, which may be connected in parallel in any desired way, are obtained in that solid granular absorber material, including zeolite, is tightly enclosed by a flexible metal or plastic sleeve so that an essentially rigid plate unit is formed. Each of these units accommodates within itself its own vapor region. An arrangement is preferred in which this vapor region extends in a central plane of the plate unit and two flat chambers are partitioned off at either side which, at the exterior faces of the plate unit, are charged by the heating or cooling heat exchange medium. For reasons of optimum heat contact with the heat exchange medium which charges the exterior of the plates, the respective chamber depth can be only very small since vapor regions and charging regions alternate with the heat exchange medium at both flat sides of the chambers and thus heat can flow into or out of the chamber only from one flat side. The narrow sides of the chambers can here be neglected. However, despite separation into individual structural units, this, involves relatively high construction costs per structural unit.